prEN 12939

SLOVENSKI STANDARD
01-december-2025
Toplotne karakteristike gradbenih materialov in proizvodov - Določanje toplotne
upornosti z zaščiteno vročo ploščo in merilniki toplotnih tokov - Debeli proizvodi z
visoko in srednjo toplotno upornostjo
Thermal performance of building materials and products - Determination of thermal
resistance by means of guarded hot plate and heat flow meter methods - Thick products
of high and medium thermal resistance
Wärmetechnisches Verhalten von Baustoffen und Bauprodukten - Bestimmung des
Wärmedurchlasswiderstandes nach dem Verfahren mit dem Plattengerät und dem
Wärmestrommessplatten-Gerät - Dicke Produkte mit hohem und mittlerem
Wärmedurchlasswiderstand
Performance thermique des matériaux et produits pour le bâtiment - Détermination de la
résistance thermique par la méthode de la plaque chaude gardée et la méthode
fluxmétrique - Produits épais de haute et moyenne résistance thermique
Ta slovenski standard je istoveten z: prEN 12939
ICS:
91.100.60 Materiali za toplotno in Thermal and sound insulating
zvočno izolacijo materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2025
ICS 91.100.60 Will supersede EN 12939:2000
English Version
Thermal performance of building materials and products -
Determination of thermal resistance by means of guarded
hot plate and heat flow meter methods - Thick products of
high and medium thermal resistance
Performance thermique des matériaux et produits Wärmetechnisches Verhalten von Baustoffen und
pour le bâtiment - Détermination de la résistance Bauprodukten - Bestimmung des
thermique par la méthode de la plaque chaude gardée Wärmedurchlasswiderstandes nach dem Verfahren mit
et la méthode fluxmétrique - Produits épais de haute et dem Plattengerät und dem Wärmestrommessplatten-
moyenne résistance thermique Gerät - Dicke Produkte mit hohem und mittlerem
Wärmedurchlasswiderstand
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 89.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 12939:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
1 Scope . 5
2 Normative references . 5
3 Terms, definitions, symbols and units . 5
3.1 Terms and definitions . 5
3.2 Symbols and units . 5
4 Apparatus . 7
4.1 General . 7
4.2 Maximum specimen thickness . 7
4.3 Minimum specimen thickness, flatness tolerances . 7
5 Procedures . 7
5.1 Specimen preparation and handling . 7
5.2 Introductory considerations . 7
5.3 The relevance of the thickness effect . 10
5.3.1 General . 10
5.3.2 Procedure for wool-type products . 10
5.3.3 Procedures for other materials . 11
5.4 Procedures when the thickness effect is not relevant . 11
5.5 Procedures when the thickness effect is relevant . 12
5.5.1 General . 12
5.5.2 Determination of the thermal transmissivity of the material . 12
5.5.3 Determination of the thermal resistance of the products . 12
6 Calculations and test report . 13
Annex A (informative) Instrumentation for the apparatus (GHP/HFM) . 16
A.1 Guarded hot plate . 16
A.1.1 Guarded hot plate apparatus requirements and equipment performance check . 16
A.2 Heat flow meter . 16
A.2.1 Heat flow meter apparatus requirements, calibration and equipment performance
check . 16
A.3 Maximum specimen thickness . 16
A.4 Minimum specimen thickness, flatness tolerances . 17
A.4.1 Thickness error and minimum specimen thickness of non rigid specimens . 17
A.4.2 Contact resistances and flatness tolerances of rigid specimens . 18
Annex B (normative) Conversion utilities for thick specimens . 19
B.1 General . 19
B.2 Interpolating functions . 19
B.2.1 Interpolating functions applicable to any product . 19
B.2.2 Interpolating functions for wool-type products . 20
B.2.3 Interpolating functions for cellular plastic materials and insulating cork boards . 21
Annex C (informative) Advanced procedures to test thick specimens exceeding thickness
capabilities of the apparatus . 23
C.1 Introductory considerations . 23
C.2 Preliminary procedures on the relevance of the thickness effect . 24
C.2.1 General . 24
C.2.2 Preliminary estimation of the relevance of the thickness effect . 25
C.2.3 Procedures to measure R and λt to assess the relevance of the thickness effect . 26
C.3 Procedures when the thickness effect is relevant . 27
C.3.1 Use of tabulated data when the thickness effect is relevant . 27
C.3.2 Experimental procedures when the thickness effect is relevant . 27
Annex D (informative) Items which are expected to be specified in product standards . 32
Bibliography . 33
European foreword
This document (prEN 12939:2025) has been prepared by Technical Committee CEN/TC 89 "Thermal
performance of buildings and building components", the secretariat of which is held by SIS.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 12939:2000.
— revision of all document to be compliant with CEN rules;
— revision of Clause 2;
— revision of Annex A.
1 Scope
This document spécifiés procedures to determine the thermal resistance of products whose thicknesses
exceed the maximum thickness for guarded hot plate or heat flow meter apparatus. Most of the
procedures described in this standard require apparatus that allows tests on specimens up to 100 mm
thick .
This document gives guidelines to assess the relevance of the thickness effect, i.e. to establish whether
the thermal resistance of a thick product can or cannot be calculated as the sum of the thermal
resistances of slices cut from the product, these guidelines complement the indications given in ISO
8302:1991[1] on the guarded hot plate apparatus.
This document describes testing conditions which prevent the onset of convection which could take
place in some products under the considered temperature differences and thicknesses.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN ISO 7345:2018, Thermal performance of buildings and building components - Physical quantities and
definitions (ISO 7345:2018)
EN ISO 9288:2022, Thermal insulation - Heat transfer by radiation - Vocabulary (ISO 9288:2022)
EN 12667, Thermal performance of building materials and products - Determination of thermal resistance
by means of guarded hot plate and heat flow meter methods - Products of high and medium thermal
resistance
EN 12667:2001, Thermal performance of building materials and products - Determination of thermal
resistance by means of guarded hot plate and heat flow meter methods - Products of high and medium
thermal resistance
3 Terms, definitions, symbols and units
3.1 Terms and definitions
For the purposes of this document, the terms and définitions given in EN ISO 7345:2018
andEN ISO 9288:2022 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses: • ISO
Online browsing platform: available at http://www.iso.org/obp
• IEC Electropedia: available at http://www.electropedia.org/
NOTE EN ISO 9288:2022[2] définés spectral directional extinction, absorption and scattering coéfficiénts and
the spectral directional albedo only, while this standard makes use of total hemispherical coéfficiénts, which can
be obtained by the previous ones by appropriate integrations.
3.2 Symbols and units
Symbol Quantity Unit
A conduction parameter W/(m.K)
B solid conduction parameter
m /kg
C radiation parameter
W·m /(kg·K)
-1
E extinction parameter for combined conduction and radiation
m
F complement to unity of the "two flux model" albedo
L thickness effect paramete K
R thermal resistance
m ·K/W
R , R , R extrapolated thermal resistance at zero thickness
m ·K/W
0 01 02
T thermodynamic temperature K
T transfer factor d/R (o
...